1. Technical Field
This present invention relates to a power management unit and a wireless power system adopting the power management unit, more specifically, to a power management unit with over-voltage protection and a wireless power system adopting the power management unit.
2. Description of Related Art
Wireless power, also known as wireless energy transmission, is a technique which takes advantage of near-field coupling, for example inductive coupling, to transmit energy from a power supplying equipment to an electric device. For example in the application of wireless charging, an electronic device receives energy via wireless power for charging a battery and providing required power for operation. Since the energy transmission between the electronic device and the power supplying equipment is realized by inductive coupling without conducting wires, no conducting point is exposed on both the electronic device and the power supplying equipment. Therefore, the danger of electric shot by contacting can be avoided, and the un-exposed metal parts can be free from oxidation by water vapor or oxygen. Besides, the mechanical degradation and the possible danger caused by spark, both of which are caused by connecting and separating the electronic device and the power supplying equipment, can also be avoided.
The technical development on wireless power brings great contribution on the medical applications and consumer electronics. The wireless power technique makes medical implant device safer. Without conducting wires penetrating skin and other body tissues, patient can charge the medical implant device without harming body tissues and free from the risk of infection. The wireless power technique also brings great convenience on consumer electronics since devices can be charged merely by being placed in the vicinity of the wireless charger, and the wires are obsoleted. Besides, technically a wireless charger can charge many electronic devices at the same time which saves wires, adaptors and power outlets.
FIG. 1 is a schema of a wireless power system 100 of prior art. The wireless power system 100 includes a wireless power transmitting end and a wireless power receiving end. The wireless power transmitting end includes a power supply 110, a supply coupling capacitor 120 and first windings 130. The wireless power receiving end includes second windings 150, input capacitor 160. The wireless power transmitting end transmits a wireless power 140 of alternating current (AC), and the wireless power receiving end receives the wireless power 140 by near-field coupling, for example (but not limited to) inductive coupling between first windings 130 and second windings 150, to generate an AC power into a rectifier 170. The rectifier 170 is adopted to rectify the received AC power into a direct-current (DC) voltage. The wireless power system 100 can further include a regulator 180 which receives the DC voltage from rectifier 170 and generates a stable output voltage to supply a load (not shown in FIG. 1). In the application of wireless charging, the regulator 180 generates a regulated output voltage or output current to charge a battery.
However, on the design of the rectifier, the converting efficiency of the rectifier 170 should be taken into consideration. As the result, a rated maximal voltage value is usually specified to the devices of the rectifier 170. If the input voltage of the rectifier 170 is higher than the rated maximal voltage value, the lifetime of the rectifier 170 will be decreased. In the worst case, the rectifier 170 is damaged directly. Nonetheless, with gradually prevailing of the wireless power technology, different wireless power standards of wireless power systems will be developed to apply to different application scenarios. Hence, it will possibly happen that a wireless power receiver with lower rated maximal voltage value is coupled to a wireless power transmitter with higher rated maximal voltage value, which causes a voltage higher than the rated maximal voltage value generated on the input port of the rectifier, and the lifetime of the wireless power receiver is decreased, or even the wireless power receiver is damaged. Therefore, there should be protection design on the wireless power receiver to prevent possible damage from the aforementioned cases.